Heat pipes have immense potential in the future of thermal management in electronic devices. As a passive device, they rely solely upon capillary forces to recirculate the coolant from the condenser to the evaporator via a wicking structure. In intermediate temperature heat pipes the limiting factor for heat removal is the capillary limit, which indicates the maximum recirculation rate that the capillary forces can induce. This capillary limit must be increased to allow heat pipes to remain a viable option for heat management within electronic devices. The aim of this work is to characterize and optimize the capillary limit of micropillared thermal wicks for heat pipe application in micro-electronics cooling.
Towards this goal, an analytical model, and a novel thermo-hydraulic experimental setup was developed. The analytical model of the micropillared array wicking structure provides a theoretical basis from which the pillar geometry and arrangement can be optimized. A capillary limit model was used to determine the geometric relationship between the pillar arrays and the maximum capillary flow rate through the wick. This model considers the effects of gravity and mass transfer due to evaporation.
Finally, the thermo-hydraulic characterization setup, designed to minimize environmental losses, was used to experimentally determine the capillary limits of different silicon based micropillared wick samples. The heater and wicking structure were enclosed in a temperature and humidity controlled vacuum chamber. The results obtained from this setup were used to validate the analytical model shown in this paper.